This invention relates to an apparatus suitable for use in the collection of plasma, and more particularly to an apparatus for separating plasma from the blood donated and also returning the remaining blood to the donor.
It is known that the blood being withdrawn from the donor can be passed through a plasma separator at increased flow rate per unit time so as to ensure separating plasma from the blood. Too high flow rate, however, is rather inapplicable as there is a prescribed limit placed on the amount of blood to be collected from the individual donor.
A more advanced system has been proposed to this end as disclosed for instance in Japenese Patent Application Laid-open No. 85950/1986. Such known system involves the collection of blood in extracorporeal circuit including a plasma separator alternately with the return of hemocytes or blood cells to the donor under instrumented and controlled conditions. The blood is separated in the plasma separator into both plasma and hemocyte fluids. The hemocyte fluid, temporarily stored in a blood reservoir, is allowed to return to the donor's vein. Blood collection, during blood return, is brought to a stop and vice versa. However, this prior art system is encountered with certain drawbacks described below.
The hemocyte fluid is a viscous fluid resulting from removal of a part of plasma from the blood and having a large volume index of hemoglobin commonly called the hematocrit value and hereinafter referred to simply as the "Ht" value. While in plasma separation, the hemocyte fluid if forced to return to the donor would enter the plasma separate. This is taken to mean that the separator would become suddenly pressurized at its inlet and outlet portions, leading to blood leakage or hemolysis hazards. This problem may be alleviated or eliminated by the return of blood cells at, reduced speed which however is literally time-consuming and totally unpractical.